Allow for bigger indices in VisitChildrenResult

The indexes stored in `VisitChildrenResult` are unsigned. We have 64
bits to store two values and we need to have one special value as a flag.

So accept any index `< u32::MAX` instead of `< i32::MAX`, which should
allow for more data to be visited;-)

api/sixtyfps-cpp/include/sixtyfps.h

@@ -695,16 +695,16 @@ public:
         viewport_height->set(h);
     }
 
-    intptr_t visit(TraversalOrder order, private_api::ItemVisitorRefMut visitor) const
+    uintptr_t visit(TraversalOrder order, private_api::ItemVisitorRefMut visitor) const
     {
         for (std::size_t i = 0; i < inner->data.size(); ++i) {
             int index = order == TraversalOrder::BackToFront ? i : inner->data.size() - 1 - i;
             auto ref = item_at(index);
-            if (ref.vtable->visit_children_item(ref, -1, order, visitor) != -1) {
+            if (ref.vtable->visit_children_item(ref, -1, order, visitor) != std::numeric_limits<uint64_t>::max()) {
                 return index;
             }
         }
-        return -1;
+        return std::numeric_limits<uint64_t>::max();
     }
 
     vtable::VRef<private_api::ComponentVTable> item_at(int i) const

sixtyfps_compiler/generator/cpp.rs

@@ -1488,7 +1488,7 @@ fn generate_component(
                 Access::Public,
                 Declaration::Function(Function {
                     name: "visit_dynamic_children".into(),
-                    signature: "(intptr_t dyn_index, [[maybe_unused]] sixtyfps::private_api::TraversalOrder order, [[maybe_unused]] sixtyfps::private_api::ItemVisitorRefMut visitor) const -> int64_t".into(),
+                    signature: "(intptr_t dyn_index, [[maybe_unused]] sixtyfps::private_api::TraversalOrder order, [[maybe_unused]] sixtyfps::private_api::ItemVisitorRefMut visitor) const -> uint64_t".into(),
                     statements: Some(vec![
                         "    auto self = this;".to_owned(),
                         format!("    switch(dyn_index) {{ {} }};", children_visitor_cases.join("")),
@@ -1616,10 +1616,10 @@ fn generate_component_vtable(
         Access::Private,
         Declaration::Function(Function {
             name: "visit_children".into(),
-            signature: "(sixtyfps::private_api::ComponentRef component, intptr_t index, sixtyfps::private_api::TraversalOrder order, sixtyfps::private_api::ItemVisitorRefMut visitor) -> int64_t".into(),
+            signature: "(sixtyfps::private_api::ComponentRef component, intptr_t index, sixtyfps::private_api::TraversalOrder order, sixtyfps::private_api::ItemVisitorRefMut visitor) -> uint64_t".into(),
             is_static: true,
             statements: Some(vec![
-                "static const auto dyn_visit = [] (const uint8_t *base,  [[maybe_unused]] sixtyfps::private_api::TraversalOrder order, [[maybe_unused]] sixtyfps::private_api::ItemVisitorRefMut visitor, uintptr_t dyn_index) -> int64_t {".to_owned(),
+                "static const auto dyn_visit = [] (const uint8_t *base,  [[maybe_unused]] sixtyfps::private_api::TraversalOrder order, [[maybe_unused]] sixtyfps::private_api::ItemVisitorRefMut visitor, uintptr_t dyn_index) -> uint64_t {".to_owned(),
                 format!("    [[maybe_unused]] auto self = reinterpret_cast<const {}*>(base);", component_id),
                 format!("    switch(dyn_index) {{ {} }};", children_visitor_cases.join("")),
                 "    std::abort();\n};".to_owned(),

sixtyfps_runtime/corelib/item_tree.rs

@@ -23,30 +23,30 @@ pub enum TraversalOrder {
 /// otherwise this is the index of the item that aborted the visit.
 #[repr(transparent)]
 #[derive(Copy, Clone, Eq, PartialEq)]
-pub struct VisitChildrenResult(i64);
+pub struct VisitChildrenResult(u64);
 impl VisitChildrenResult {
     /// The result used for a visitor that want to continue the visit
-    pub const CONTINUE: Self = Self(-1);
+    pub const CONTINUE: Self = Self(u64::MAX);
 
     /// Returns a result that means that the visitor must stop, and convey the item that caused the abort
     pub fn abort(item_index: usize, index_within_repeater: usize) -> Self {
-        assert!(item_index < i32::MAX as usize);
+        assert!(item_index < u32::MAX as usize);
-        assert!(index_within_repeater < i32::MAX as usize);
+        assert!(index_within_repeater < u32::MAX as usize);
-        Self(item_index as i64 | (index_within_repeater as i64) << 32)
+        Self(item_index as u64 | (index_within_repeater as u64) << 32)
     }
     /// True if the visitor wants to abort the visit
     pub fn has_aborted(&self) -> bool {
-        self.0 != -1
+        self.0 != Self::CONTINUE.0
     }
     pub fn aborted_index(&self) -> Option<usize> {
-        if self.0 != -1 {
+        if self.0 != Self::CONTINUE.0 {
             Some((self.0 & 0xffff_ffff) as usize)
         } else {
             None
         }
     }
     pub fn aborted_indexes(&self) -> Option<(usize, usize)> {
-        if self.0 != -1 {
+        if self.0 != Self::CONTINUE.0 {
             Some(((self.0 & 0xffff_ffff) as usize, (self.0 >> 32) as usize))
         } else {
             None
@@ -55,7 +55,7 @@ impl VisitChildrenResult {
 }
 impl core::fmt::Debug for VisitChildrenResult {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        if self.0 == -1 {
+        if self.0 == Self::CONTINUE.0 {
             write!(f, "CONTINUE")
         } else {
             write!(f, "({},{})", (self.0 & 0xffff_ffff) as usize, (self.0 >> 32) as usize)